Back in 2001, a generous fellow named Marius Milner gave the world a utility called Netstumbler and a new culture was born. Milner is a software engineer who did the rare thing for his fellow man: he gave away a kicking program that he likely could have made some serious dollars from if he had sold it. Even better, he provided updates to Netstumbler through the years, along with a discussion forum that would become a repository for a wealth of information regarding wireless networking in general.
MiniStumbler was provided for handheld devices, and the ability to find and characterize wireless networks was turned into a quasi-sport that would be dubbed 'Wardriving." Netstumbler would also become a valued tool for survey and troubleshooting work in countless WLANs. The interface is simple but effective and has stood the test of time. I have used it hundreds of time on the job, during demonstrations and in the classroom for teaching wireless.
As slick as Milner's baby is, there are shortcomings to Netstumbler. Some chipsets are not compatible, it can't show hidden SSIDs and it doesn't show interfering non-WiFi devices. But the price is right, and NetStumbler showed the world the sort of tool that could be developed, easily installed and used in the dominant world of Microsoft Windows, which is toted around on laptops as new wireless admins got their sea legs. (Sure, those of us who "do" Linux have always had a wealth of wireless tools at our disposal, but we're in the minority).
Netstumbler paved the way for a handful of big name pay-to-play tools, like AirMagnet, Wild Packet's AeroPeek and several tools in the Fluke Networks' wireless arsenal to expand greatly on the basic notion of wireless stumbling. There's absolutely nothing wrong with paying for a good tool that brings value, and the choices of wireless support software available for today's 802.11n-centric world are a wireless geek's dream. But free gems are still out there, and Milner is no doubt smiling about it.
One big difference between Netstumbler and the latest whiz-bang freebies is who's offering them up. Another is their level of sophistication and functionality that many of us would not mind shelling out a bit for. Xirrus Networks' powerful Wi-Fi Inspector is one of the latest in a generation of complimentary tactical tools that may well be beefy enough to negate the need for pricier tools if placed in skilled hands. Meraki also provides a superb update to the basic stumbling model with its browser-based Wi-Fi Stumbler and Wi-Fi Mapper tools, again, at no cost and with killer feature sets. Ekahau, whose sight survey and modeling tools are among my favorite paid utilities, provides the no-cost HeatMapper utility. The first time you use HeatMapper properly, you'll be blown away by the survey-oriented views provided. These are my favorites, but there are certainly others out there. Xirrus, Ekahau, and Meraki want your wireless business, and the free tools are meant to get your attention. And well they should. These things are dynamite. Sure, Milner might have been more altruistic with his motives, but the modern versions of his ideals are too sweet not use, regardless of why they are being provided.